A “spun-laid” process, as used herein, refers to a process in which one or more polymers are melted, extruded, air quenched, drawn (for example, by air, godet rolls and/or any other types of suitable devices), and deposited as solidified fibers onto a suitable laydown or support surface (such as a porous belt) to form one or more nonwoven layers of fibers (also referred to herein as a “spun-laid web”). An example of one type of a so-called “closed system” spun-laid process is described by U.S. Pat. No. 7,179,412, the disclosure of which is incorporated herein by reference in its entirety, where attenuation of the extruded fibers is in large part created by acceleration of the same air used to quench the fibers. Another example is a so-called “open system” as described by U.S. Pat. No. 6,183,684, the disclosure of which is incorporated herein by reference in its entirety, where the attenuation of the extruded fibers is in large part created by a compressed air aspirator. In an open system, there may be only one curtain of fibers from a single spinneret and only one air aspirator, or there may be several spinnerets and several air aspirators in the cross-direction (CD) and/or machine direction (MD). In both systems, fibers covering a width up to several meters wide are deposited onto a similar width porous belt. The velocity of the fibers is usually several times the velocity of the porous belt. In addition, a fabric is typically formed having fibers oriented more in the direction of the porous belt travel (so called Machine Direction or “MD”) than in the direction perpendicular to the direction of the porous belt travel (so called Cross-Direction or “CD”).
The nonwoven web of fibers formed by conventional open and closed spun-laid systems does not result in a strong fabric. Fabric strength is typically imparted by another processing step to produce a bonded fabric, resulting in the so called “spunbond” process and spunbond web of fibers. The most common bonding technique used in spunbond processes is thermal bonding. In thermal bonding, a strong web is produced by subjecting the web to heat sufficient to partially melt some fibers or portions of some fibers to form a bound between the fibers on re-solidification. Thermal bonding includes calender bonding as well as through air bonding. In calender bonding, the nonwoven web is processed between at least two nip rolls, at least one of which is heated to a temperature sufficient to at least partially melt at least the surface of some fibers while subjecting the web to pressure between the rolls. Thermal bonding also includes the so called through air bonding technique where air is sufficiently heated and passed through the web to partially melt at least the surface of some fibers. Other known bonding techniques involve applying mechanical forces to the web sufficient to tangle or interlock the fibers to form a strong web. Such processes include needling and hydroentangling, both of which make a more three-dimensional nonwoven spunbond web as some fibers are caused to protrude from the surface. All of these bonding techniques require use of expensive and energy intensive additional machinery.
For a number of reasons, it is desirable to make a spun-laid web of fibers having sufficient bulkiness and loft (increased thickness or increase in “Z” dimension). Needling and hydroentangling processes can provide some level of bulkiness and loft but only in a relatively modest amount. Attempts have been made to make spunbond fabrics more lofty and bulky via spinning of multi-component fibers (i.e. fibers consisting of multiple discrete polymer constituents in the fiber cross section, such as bicomponent fibers) in which two or more polymer constituents have differential strain or differential shrinkage to impart curling or bending of the fibers in the web after thermal and/or mechanical treatment. An example of suitable processing apparatus for producing multi-component fibers is described, for example, in U.S. Pat. No. 5,162,074, the disclosure of which is incorporated herein by reference in its entirety. Thermal or mechanical treatment of such fibers to induce curling and/or bending of the fibers typically is performed after bonding of the web of fibers has occurred. Such processes have only been moderately successful in producing enhanced loftiness and bulk in the spunbond web, due in part to the weak or restrained bending forces normally inherent in such processes (since the fibers in the bonded web are restrained from movement and do not have the power to bend).
It is also desirable to manufacture a more uniform fabric in both appearance and physical properties. For example, techniques are known for controlled management of the large amount of air involved in the Spunbond process, particularly in open systems. Such air management is difficult and has proved to be a significant limitation in making more uniform Spun Bond fabrics.
It is further desirable to produce spunbond fabrics that are stretchy using, for example, special elastomeric polymers (such as TPU and Krayton®) in producing the fibers for the spunbond web. However, such special elastomeric polymers tend to be more expensive than normal, conventional spunbond polymers. In addition, elastomeric polymers are generally more difficult to process due to issues such as “tackiness” of the fibers and the low spinning speeds (i.e., the speed that extruded filaments attain between the spinneret and the lay down surface) typically required to process such polymers. The resultant fabrics formed utilizing such polymers can also have certain deficiencies, such as a tacky hand, difficulty and impossibility to dye with colors. Utilizing such special elastomeric polymers can also result in fabrics formed that tend to exhibit considerably more stretch in the MD than in the CD.